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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 73 records · Page 4

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NASA NTRS1975

Wind-tunnel investigation of surface-pressure fluctuations associated with aircraft buffet

Fluctuating pressures and forces that cause aircraft buffeting have been measured on a semispan rigid-wing model of a typical variable-sweep fighter-type aircraft at transonic speeds. The rms spectral and spatial correlation characteristics of wing fluctuating pressures, fluctuating pressure summations, and structural responses are presented and discussed for a Mach number of 0.85, wing sweep angles of 26 and 72 deg, and angles of attack up to 12 deg. The fluctuating pressure characteristics beneath wing shock waves and leading-edge vortices and in regions of attached and separated flows are presented. Results indicate that: (1) the mean and fluctuating static pressure characteristics are related; (2) a circulation oscillation exists for attached flow conditions below buffet onset; and (3) a significant coupling exists between the wing shock-wave oscillation and the wing first torsional mode when shock-induced separation is present.

Riddle, D. W.↗

NASA NTRS1976

Measurements of spectral and total emittance of reinforced carbon-carbon

Elevated temperature measurements of the spectral emittance of reinforced carbon-carbon (RCC) as the thermal protection material for the leading edge areas of the Space Shuttle Orbiter were carried out in situ, with environments provided by arc-heated streams of air and argon. A monochromator, infrared pyrometers, and thermocouples were used in evaluating the response of the RCC test specimens during the emittance measurements. Results indicate that the material is nongray, with lowest spectral emittance at the short wavelengths and with relatively high total emittance. The trend of the total emittance data suggests a slight decrease in total emittance with increasing temperature, although the emittance value stabilizes with continuing exposure.

Grinberg, I. M.↗

NASA NTRS2014

The Magnetically-Tuned Transition-Edge Sensor

We present the first measurements on the proposed magnetically-tuned superconducting transition-edge sensor (MTES) and compare the modified resistive transition with the theoretical prediction. A TES's resistive transition is customarily characterized in terms of the unit less device parameters alpha and beta corresponding to the resistive response to changes in temperature and current respectively. We present a new relationship between measured IV quantities and the parameters alpha and beta and use these relations to confirm we have stably biased a TES with negative beta parameter with magnetic tuning. Motivated by access to this new unexplored parameter space, we investigate the conditions for bias stability of a TES taking into account both self and externally applied magnetic fields.

Sadleir, John E.↗

NASA NTRS1992

The effect of a turbulent wake on the stagnation point. II - Heat transfer results

A phenomenological model is proposed which relates the effects of freestream turbulence to the increase in stagnation point heat transfer. The model requires both turbulence intensity and energy spectra as inputs to the unsteady velocity at the edge of the boundary layer. The form of the edge velocity contains both a pulsation of the incoming flow and an oscillation of the streamlines. The incompressible unsteady and time-averaged boundary layer response is determined by solving the momentum and energy equations. The model allows for arbitary two-dimensional geometry, however, results are given only for a circular cylinder. The time-averaged Nusselt number is determined theoretically and compared to existing experimental data.

Hanford, Anthony J.↗

NASA NTRS1995

Reflection and transmission of GMIR shock at the heliopause and their relation to the 2- and 3-kHz radio emissions

We use Voyager 2 plasma and magnetic field data together with a one-fluid MHD model to study the interactions of the 1991 Global Merged Interaction Region (GMIR) shock with the heliopause. The 1991 GMIR is an extraordinarily large global solar wind structure in radial, longitudinal and latitudinal extents. It has a strong shock at the leading edge. After its penetration through the termination shock, the GMIR shock first propagates through the subsonic solar wind, then interacts with the heliopause. The interaction produces a transmitted shock propagating outward in the interstellar medium, and a reflected shock propagating backward in the subsonic solar wind. We identify the reflected shock and the transmitted shock as the possible source of the radio noise detected at Voyagers. The plasma frequency behind the reflected and the transmitted shock can be, respectively, responsible for the 2- and 3-kHz radio emissions. The two bands of radio noise are emitted from sources on both sides of the heliopause starting at about the same time. If the emission is generated by f(sub p)-radiation then the heliopause is located at R approximately 130 AU. If the emission is generated by 2f(sub p)-radiation the n R approximately 150 AU. Because the relative speed of the interstellar plasma with respect to the sun appears to be sub-Alfvenic, it is very unlikely there is a fast-bow shock of the heliosphere.

Whang, Y. C.↗

NASA NTRS1990

Finite element thermo-viscoplastic analysis of aerospace structures

The time-dependent thermo-viscoplastic response of aerospace structures subjected to intense aerothermal loads is predicted using the finite-element method. The finite-element analysis uses the Bodner-Partom unified viscoplastic constitutive relations to determine rate-dependent nonlinear material behavior. The methodology is verified by comparison with experimental data and other numerical results for a uniaxially-loaded bar. The method is then used (1) to predict the structural response of a rectangular plate subjected to line heating along a centerline, and (2) to predict the thermal-structural response of a convectively-cooled engine cowl leading edge subjected to aerodynamic shock-shock interference heating. Compared to linear elastic analysis, the viscoplastic analysis results in lower peak stresses and regions of plastic deformations.

Pandey, Ajay K.↗

NASA NTRS1990

Finite-element thermo-viscoplastic analysis of aerospace structures

Pandey, Ajay↗

NASA NTRS1988

Fatigue testing and damage development in continuous fiber reinforced metal matrix composites

A general overview of the fatigue behavior of metal matrix composites (MMC) is presented. The first objective is to present experimental procedures and techniques for conducting a meaningful fatigue test to detect and quantify fatigue damage in MMC. These techniques include interpretation of stress-strain responses, acid etching of the matrix, edge replicas of the specimen under load, radiography, and micrographs of the failure surfaces. In addition, the paper will show how stiffness loss in continuous fiber reinforced metal matrix composites can be a useful parameter for detecting fatigue damage initiation and accumulation. Second, numerous examples of how fatigue damage can initiate and grow in various MMC are given. Depending on the relative fatigue behavior of the fiber and matrix, and the interface properties, the failure modes of MMC can be grouped into four categories: (1) matrix dominated, (2) fiber dominated, (3) self-similar damage growth, and (4) fiber/matrix interfacial failures. These four types of damage will be discussed and illustrated by examples with the emphasis on the fatigue of unnotched laminates.

Johnson, W. S.↗

NASA NTRS1989

Fatigue testing and damage development in continuous fiber reinforced metal matrix composites

Johnson, W. S.↗

NASA NTRS1980

Image contrast of diffraction-limited telescopes for circular incoherent sources of uniform radiance

A simple approximate formula is derived for the background intensity beyond the edge of the image of uniform incoherent circular light source relative to the irradiance near the center of the image. The analysis applies to diffraction-limited telescopes with or without central beam obscuration due to a secondary mirror. Scattering off optical surfaces is neglected. The analysis is expected to be most applicable to spaceborne IR telescopes, for which diffraction can be the major source of off-axis response.

Shackleford, W. L.↗

NASA NTRS1994

Interaction of global merged interaction region shock with the heliopause and its relation to the 2- and 3-kHz radio emissions

We use the Voyager 2 plasma and magnetic field data together with a one-fluid magnetohydrodynamics model to study the interactions of the 1991 global merge interaction region (GMIR) shock with the termination shock and the heliopause. The 1991 GMIR is an extraordinarily large global solar wind structure in radial, longitudinal, and latitudinal extents. It has a strong shock at the leading edge. After its penetration through the termination shock, the GMIR shock first propagates through the subsonic solar wind, then interacts with the heliopause. The interaction produces a transmitted shock propagating outward in the interstellar medium, and a reflected shock propagating backward in the subsonic solar wind. We identify the reflected shock and the transmitted shock as the possible source of the radio noise detected at Voyagers (Gurnett, et al., 1993). The plasma frequency behind the reflected and the transmitted shock can be responsible for the 2- and 3-kHz radio emissions, respectively. The two bands of radio noise are emitted from sources on both sides of the heliopause starting at about the same time. If the emissions picked up by Voyager are due to f(sub P) radiation, then the heliopause is located at R is approximately = 130 AU. If the emissions are due to 2f(sub P) radiation, the R is approximately 150 AU. Because the relative speed of the interstellar plasma with respect to the sun appears to be sub-Alfvenic, it is very unlikely there is a fast-mode bow shock of the heliosphere.

Whang, Y. C.↗

NASA NTRSDate not supplied

Simulating Meteor Ablation at the Hypersonic Materials Environmental Test System

The ablation mechanisms of stony meteorite material and a terrestrial analog were investigated at the Hypersonic Materials Environmental Test System (HyMETS) facility at NASA’s Langley Research Center. The primary analyte (Tamdakht-H5) and arc-jet test conditions were chosen to simulate the entry of an ordinary chondrite through the Earth’s mesosphere. Basalt was selected to compare the meteorite response against material with enhanced polymerization and an elevated concentration of volatile species. The initial ablation process for each material commences with the vaporization of volatile species and germination of a viscous melt layer on the stagnation surface. However, each material exhibited distinct mass loss mechanisms, with basalt recessing at twice the rate of Tamdakht. Inspection of high-speed video and chemical analysis of the post-test melt layer suggests the dominant mode of mass loss of Tamdakht is expressed through the vaporization of volatile compounds. Vaporization rates of Tamdakht are 18x higher than basalt under the most severe test conditions which provides enhanced thermal shielding. Furthermore, Tamdakht produces a relatively stable melt flow, as evidenced by perpetual growth at the sidewall and the exiguous detachment of molten material into the flow. The ablation mechanism of basalt is markedly different from Tamdakht and is governed by volatile species in the virgin material. The dominant mode of mass loss for basalt is attributed to the detachment of large sections of the stagnation surface near the edge radius. An additional but subordinate mode of mass loss is assigned to the removal of melt flow as it passes over the edge radius, where shear forces overcome the rheological properties of the molten matter. Finally, mechanistic details will be discussed in terms of designing future test campaigns, developing meteorite-based materials response models, and impacting the broader scope of the Asteroid Threat Assessment Project (ATAP).

Meteor Ablation↗

NASA NTRS2012

Variability of Jupiter's Five-Micron Hot Spot Inventory

Global upheavals on Jupiter involve changes in the albedo of entire axisymmetric regions, lasting several years, with the last two occurring in 1989 and 2006. Against this backdrop of planetary-scale changes, discrete features such as the Great Red Spot (GRS), and other vortices exhibit changes on shorter spatial- and time-scales. We track the variability of the discrete equatorial 5-micron hot spots, semi-evenly spaced in longitude and confined to a narrow latitude band centered at 6.5degN (southern edge of the North Equatorial Belt, NEB), abundant in Voyager images. Tantalizingly similar patterns were observed in the visible (bright plumes and blue-gray regions), where reflectivity in the red is anti-correlated with 5-microns thermal radiance. Ortiz et al. (1998, GRL, 103) characterized the latitude and drift rates of the hot spots, including the descent of the Galileo probe at the southern edge of a 5-micron hot spot, as the superposition of equatorial Rossby waves, with phase speeds between 99 - 103m/s, relative to System III. We note that the high 5-micron radiances correlate well but not perfectly with high 8.57-micron radiances. Because the latter are modulated primarily by changes in the upper ammonia (NH3) ice cloud opacity, this correlation implies that changes in the ammonia ice cloud field may be responsible for the variability seen in the 5-~m maps. During the NEB fade (2011 - early 2012), however, these otherwise ubiquitous features were absent, an atmospheric state not seen in decades. The ongoing NEB revival indicates nascent 5-~m hot spots as early as April 2012, with corresponding visible dark spots. Their continuing growth through July 2012 indicates the possit.le re-establishment of Rossby waves. The South Equatorial Belt (SEB) and NEB revivals began similarly with an instability that developed into a major outbreak, and many similarities in the observed propagation of clear regions.

Yanamandra-Fisher, Padma A.↗

NASA NTRS1990

Unsteady inviscid and viscous computations for vortex-dominated flows

The unsteady supersonic flow around a rigid sharp-edged delta wing is solved using the unsteady Euler and thin-layer Navier-Stokes equations. The problem is formulated relative to a moving frame of reference so that computation of the grid motion is not required. A three-dimensional, implicit, aproximately factored, central-differencing, finite-volume scheme is used to obtain the time-accurate, unsteady, locally conical flow. The inviscid and viscous results are compared during the periodic response of a wing undergoing forced rolling-oscillation motion. The results show substantial differences in the surface pressure results and other distributed flow characteristics. These differences are attributed to the inviscid and viscous flow predictions in the vortex-dominated regions. The results of the total loads do not show any significant differences.

Kandil, Osama A.↗

NASA NTRS1974

Polarized electromagnetic response of the moon

The strong anisotropy in Apollo 15 Lunar Surface Magnetometer (LSM) signals resulting from electromagnetic induction in the moon, forced by fluctuations of the interplanetary magnetic field, is shown to result from intense polarization of the induced field. Arguments are given to show that the anisotropy cannot be explained wholly by asymmetric lunar induction in the presence of the diamagnetic cavity, but must be related to a regional influence. The weaker Apollo 12 anisotropy may also be associated with a regional influence. The site of Apollo 15 LSM at the edge of the Imbrium Basin suggests a preliminary model for calculations based on the possibility that Imbrium and perhaps Serenitatis are sources of the regional effect. Lastly, since the very low frequency induction seems free of the anisotropy, our earlier estimate of deep conductivity remains unchanged.

Sonett, C. P.↗

NASA NTRS1998

Buckling and Damage Resistance of Transversely-Loaded Composite Shells

Experimental and numerical work was conducted to better understand composite shell response to transverse loadings which simulate damage-causing impact events. The quasi-static, centered, transverse loading response of laminated graphite/epoxy shells in a [+/-45(sub n)/O(sub n)](sub s) layup having geometric characteristics of a commercial fuselage are studied. The singly-curved composite shell structures are hinged along the straight circumferential edges and are either free or simply supported along the curved axial edges. Key components of the shell response are response instabilities due to limit-point and/or bifurcation buckling. Experimentally, deflection-controlled shell response is characterized via load-deflection data, deformation-shape evolutions, and the resulting damage state. Finite element models are used to study the kinematically nonlinear shell response, including bifurcation, limit-points, and postbuckling. A novel technique is developed for evaluating bifurcation from nonlinear prebuckling states utilizing asymmetric spatial discretization to introduce numerical perturbations. Advantages of the asymmetric meshing technique (AMT) over traditional techniques include efficiency, robustness, ease of application, and solution of the actual (not modified) problems. The AMT is validated by comparison to traditional numerical analysis of a benchmark problem and verified by comparison to experimental data. Applying the technique, bifurcation in a benchmark shell-buckling problem is correctly identified. Excellent agreement between the numerical and experimental results are obtained for a number of composite shells although predictive capability decreases for stiffer (thicker) specimens which is attributed to compliance of the test fixture. Restraining the axial edge (simple support) has the effect of creating a more complex response which involves unstable bifurcation, limit-point buckling, and dynamic collapse. Such shells were noted to bifurcate into asymmetric deformation modes but were undamaged during testing. Shells in this study which were damaged were not observed to bifurcate. Thus, a direct link between bifurcation and atypical damage could not be established although the mechanism (bifurcation) was identified. Recommendations for further work in these related areas are provided and include extensions of the AMT to other shell geometries and structural problems.

Wardle, Brian L.↗

NASA NTRS1973

Versatile logic system for use in nuclear experiments on scientific satellites.

An improved fast low-power-drain logic system has been developed for use in nuclear experiments on scientific satellites. The basic unit of the system is an AND-NAND gate which has a response in the 10-nsec range, a power drain of 2.0 mw and operates over the temperature range of -40 to +80 C. In addition to providing the AND-NAND logic functions, one or more of the basic units may be connected to yield a monostable pulse generator, a pulse generator proceeding an output pulse at the leading edge of the input pulse, a delay, a threshold detector, and a bistable circuit. The system requires relatively simple circuitry for interfacing at its outputs and inputs.

Cancro, C. A.↗

NASA NTRS2018

Aerosol-Radiation-Cloud Interactions in the South-East Atlantic: Results from the ORACLES-2016 Deployment and a First Look at ORACLES-2017 and Beyond

Seasonal biomass burning (BB) in Southern Africa during the Southern hemisphere spring produces almost a third of the Earth's BB aerosol particles. These particles are lofted into the mid-troposphere and transported westward over the South-East (SE) Atlantic, where they interact with one of the three semi-permanent subtropical stratocumulus (Sc) cloud decks in the world. These interactions include adjustments to aerosol-induced solar heating and microphysical effects. The representation of these interactions in climate models remains highly uncertain, because of the scarcity of observational constraints on both, the aerosol and cloud properties, and the governing physical processes. The first deployment of the NASA P-3 and ER-2 aircraft in the ORACLES (ObseRvations of Aerosols Above Clouds and Their IntEractionS) project in August/September of 2016 has started to fill this observational gap by providing an unprecedented look at the SE Atlantic cloud-aerosol system. We provide an overview of the first deployment, highlighting aerosol absorptive and cloud-nucleating properties, their vertical distribution relative to clouds, the locations and degree of aerosol mixing into clouds, cloud changes in response to such mixing, and cloud top stability relationships to the aerosol. We also expect to describe preliminary results of the second ORACLES deployment from Sao Tome and Principe in August 2017. We will make an initial assessment of the differences and similarities of the BB plume and cloud properties as observed from a deployment site near the plume's northern edge. We will conclude with an outlook for the third ORACLES deployment in October 2018.

Redemann, Jens↗